And in fact, even if all that were not an issue lets thinks for a moment, its a bit nonsensical as an upgrade.. since, what would be the benefit of improving the camera lets say, 3, ..5, 10 MP more? and then? whats the deal? what do we gain by having more pixels. Especially, since all the quality that visually surrounds a the photo, takes place in the software part, and where the same sensor, could with the necessary bits of software deliver, DSLR class (well, not really, but imitating lets say) pictures.
While! If we were considering for example a camera sensor with depth or even 3D sensing, then, yea... now we are talking,.. maybe it could even justify all these points and the figures etc, for example.
But my point to the OP, I'm not sure I can really see how the mainstream buyer would ever pay attention at all to the camera, even in case it didn't exist at all. And think about this: the iphones, for years now, systematically are equipped with sensors 5-10 MP less than todays standards sensors you find in android or windows phones. Did that stop any iphone buyer from buying an iphone?